A power module used in a vehicle inverter and the like has hitherto been constituted of electronic components shown in FIG. 9. Specifically, a power module 70 at least includes a power element 71 made of a silicon element, an insulating member 73 made of aluminum nitride to which the power element 71 is fixed through a solder layer 72, and a heat sink member 74 made of aluminum. Further, between the insulating member 73 and the heat sink member 74, a buffer member 75 made of copper-molybdenum (Cu—Mo) or aluminum-silicon carbide (Al—SiC) is installed for the purpose of transmitting a heat generated from the power element 71 to the heat sink member 74 and dissipating the heat as well as for the purpose of alleviating the difference in thermal expansion between the insulating member 73 and the heat sink member 74. The buffer member 75 is fixed to the insulating member 73 by a solder layer 76, and is fixed to the heat sink member 74 by a silicon grease 77. As thus described, the buffer member 75 in combination with the heat sink member 74 constitutes a thermal conduction member for dissipating the heat from the power element 71.
However, in the power module 70, the silicon grease 77 that fixes the buffer member 75 has lower thermal conductance than those of the other members, and has thus been an obstacle in transmission of the heat from the power element 71 to the heat sink member 74. In order to avoid this, for example, a method can be considered in which copper-molybdenum (Cu—Mo) is metallized directly on the surface of the heat sink member 74 without using the silicon grease 77, to form the buffer member 75 as a film. However, since the metal powder is melt and the melt metal is further sprayed to the substrate in this method, the film is significantly oxidized and the substrate is also significantly thermally affected, whereby the method cannot be the to be preferred.
Thereat, a film forming method called cold spraying has recently been proposed. This cold spraying is a method of increasing a flow rate of a compressed gas heated to a temperature lower than a melting point or a softening temperature of a material for the film by use of a tapered and widened (laval) nozzle, putting a powder as the material for the film into the gas flow for acceleration, and colliding the powder remaining in a solid-phase state with the substrate at a high rate, to form a film (e.g. see JP Patent Publication (Kokai) NO. 6-37438A (1994)).